Braking systems with cooling

ABSTRACT

A braking system includes an axle, a support element mounted on the axle, a brake ring connected to the periphery of the support element and a brake calliper for applying a braking force to the brake ring. The brake ring is connected to the support element in such a manner that a conductive heat flow path is provided for conducting heat from the brake ring into the support element. There is also an airflow path passing through the support element and through the region in which the brake calliper is situated for transferring heat by convection from the brake ring and the brake calliper.

This invention relates to braking systems particularly, but notexclusively, for vehicle wheels.

Braking systems for vehicle wheels generally function by convertingkinetic energy into heat energy using a braking system which includes asurface with a high coefficient of friction to slow down the wheels. Theproblem is that if the generated heat is not dissipated, the brakingefficiency of the systems becomes less and less, and eventually thebrakes fail through so-called brake fade.

Drum brakes are particularly vulnerable to brake fade because more ofthe drum is heated by the friction generating shoes than is available todissipate heat by convection to the surrounding air.

Disc brakes are generally more efficient than drum brakes because theyenable greater pressure to be applied by a calliper squeezing brake padson to a brake disc attached to the associated wheel hub than can beapplied to the internal surface of the drum of a drum brake. The area ofheating contact between the friction pads of disc brakes and theirassociated discs can therefore be substantially reduced compared withthat of brake shoes with their associated drums for the same brakingeffort. Typically, 20% of the surfaces of the discs of disc brakes areintensely heated by disc pads, with 80% of the disc being available todissipate heat by convection to the surrounding air within the confinesof the associated wheel.

In an attempt to improve their vehicle braking systems, manufacturershave been increasing the internal diameters of the wheels of theirvehicles so that larger diameter discs and larger brake callipers can befitted. This can enable the braking leverage of braking systems to beincreased as a result of the increased disc radius. However, the largerradius of these larger discs means that the associated calliper has tobe considerably longer than with the conventional smaller discs to coverthe depth of the discs.

The longer so-called “beam” callipers used with these larger discs aregenerally of four or six pot construction, and this adds considerably totheir complexity and cost of production. In addition, they greatlyreduce the area of the brake disc which is exposed for cooling byconvection to air inside the wheel, and they can also worsen the “plug”effect by reducing the air space available to cool the discs byconvection of air inside the associated wheel.

The main inherent problem with both drum and disc braking systems is,therefore, that heat dissipation from them by convection through the airalone is generally insufficient to prevent brake fade. Furthermore, thevery designs of the braking systems themselves tend to reduce theirefficiency by disrupting airflow over surfaces which should serve tocool these surfaces.

It is an object of the invention to provide a braking system which canbe cooled particularly well and exhibit high and prolonged performance.

According to the invention there is provided a braking system comprisingan axle, a support element mounted on the axle, a brake ring connectedto the periphery of the support element and a brake calliper forapplying a braking force to the brake ring, the brake ring beingconnected to the support element in such a manner that a conductive heatflow path is provided for conducting heat from the brake ring into thesupport element and there being an airflow path passing through thesupport element and through the region in which the brake calliper issituated for transferring heat by convection from the brake ring and thebrake calliper.

By cooling the braking arrangement both by conduction of heat from thering into the support element and by convection cooling of the supportelement, the ring and the brake calliper, it becomes possible to providea braking system with good cooling and high performance, even withprolonged braking.

The braking system may be applied to a wheel of a vehicle, for example acar. The wheel may include a hub and the support element. The supportelement may extend from the hub to the brake ring. The brake ring mayform part of, or be connected to, the rim of the wheel.

Whilst it is within the scope of the invention to rely on cooling aircurrents being generated by convection or other factors, the brakingsystem preferably includes air current generating means for creating aflow of air along the airflow path. For example, vanes may be providedfor creating the flow of air along the airflow path. The vanes may formpart of the support element. In one embodiment of the invention thevanes may be provided in the hub of the wheel. In another embodiment ofthe invention the vanes may be provided in an element, which may be thesupport element, extending outwardly from an axle.

In order to provide an effective airflow path passing through thesupport element, the support element preferably has openings occupying alarge proportion of its cross-sectional area. Preferably, at least 200%,and more preferably at least 40%, of the cross-sectional area of thesupport element comprises one or more openings to allow airflow throughthe support element.

The brake ring may be detachably connected to the support element or itmay be integral with the support element. In either case, there shouldbe a good conductive path for conducting heat from the brake ring intothe support element. Accordingly, the interface of the brake ring andthe support element preferably comprises a continuous annular interface.The interface preferably has a cross-sectional area that is at least 20%and preferably more than 50% of the cross-sectional area of the brakering immediately upstream of the interface. Thus heat flowing to theinterface from the brake ring suffers not more than a 50% reduction inthe cross-sectional area available for the conduction of heat.

Preferably the brake ring projects radially inwardly from the peripheryof the support element. In that case the brake calliper is situated tothe inside of the brake ring, enabling the brake ring to be of a greaterdiameter. Preferably, the brake ring is planar and is in a planeperpendicular to the axis of rotation.

As well as cooling by ordinary air convection, it is within the scope ofthe invention to provide an enclosed region around a part of the brakering and/or the brake calliper and to feed fluid into the region andremove fluid from the region. Such an arrangement can enable moreefficient heat exchange into the fluid, which may be a refrigerant andmay be recirculated.

In the aspect of the invention defined above, a preferred form ofbraking system is defined. It is however possible to provide a brakingsystem in accordance with the invention that comprises a differentselection of the features defined above. According to a broad aspect ofthe invention, there is provided a braking system comprising an axle, asupport element mounted on the axle, a brake ring connected to theperiphery of the support element and a brake calliper for applying abraking force to the brake ring, the system further including one ormore of the following features:

-   -   (i) the brake ring is connected to the support element in such a        manner that a conductive heat flow path is provided for        conducting heat from the brake ring into the support element;    -   (ii) there is an airflow path passing through the support        element and through the region in which the brake calliper is        situated for transferring heat by convection from the brake ring        and the brake calliper;    -   (iii) the support element is part of a wheel;    -   (iv) the braking system includes air current generating means        for creating a flow of air along the airflow path;    -   (v) the brake ring is integral with the support element;    -   (vi) the brake ring is planar and is in a plane perpendicular to        the axis of rotation of the axle;    -   (vii) the braking system includes a refrigerant system for        cooling the braking system.

The braking system according to the broad aspect of the invention mayfurther incorporate any of the other features defined above.

The braking system may be used in a wide variety of applicationsincluding, but not limited to, various vehicles. Examples of theinvention including cars, including racing cars, trains and aircraft aredescribed below.

By way of example, embodiments of the invention will now be describedwith reference to the accompanying schematic drawings, in which:

FIG. 1 is a vertical section through a braking system applied to aconventional car wheel;

FIG. 2 is a perspective view from the outside of a vehicle wheel that isa modified form of the wheel of FIG. 1;

FIG. 3 is a perspective view from the inside of the wheel of FIG. 2 witha brake ring attached to the wheel;

FIG. 4 is a sectional view of a car wheel axle assembly with a modifiedform of braking system;

FIG. 5 is a perspective view of a train axle with a braking system; and

FIG. 6 is a schematic perspective view of a braking system for a vehiclewheel, including a refrigerant system.

The car vehicle wheel shown in FIG. 1 is generally conventional in thatit has fixing holes 1 for securing it to an axle of the vehicle and asupport element 9 including a rim 2 for receiving a pneumatic tyre (notshown). However, it differs from conventional vehicle wheels in that itincludes an annular brake ring 3 which is secured in an annular recess 4in the rim 2 by countersunk bolts 5. Also the support element 9 thatextends from the central part of the wheel to the rim 2 is provided withmany openings 10.

Braking forces can be applied to the brake ring 3 using a calliper 6which is attached to the vehicle suspension and can be operatedhydraulically in conventional manner via an hydraulic hose (not shown)to force hydraulic pistons against brake pads 8, and the latter intofrictional engagement with the ring 3.

In use air currents pass over the brake calliper 6 and the brake ring 3and through the openings 10 taking heat generated during braking awayfrom those parts. Also, heat generated in the brake ring 3 flows throughthe interface with the rim 2 into the rim part of the support element 9.The connection of the brake ring 3 to the rim 2 is the same around allthe periphery of the wheel with the bolts 5 provided at intervals. Thusa conductive heat flow path is provided for the ring 3 into the supportelement 9.

In the particular example shown, the cross-sectional area of theinterface of the brake ring and the support element 9 is as great as thecross-sectional area of the brake ring immediately upstream of theinterface. Thus provided the ring 3 and support element 9 are made ofthermally conductive material and there is good thermal contact at theinterface, a good conductive heat flow path is formed for conductingheat from the brake ring 3 into the support element 9. In the embodimentshown in FIG. 1 the openings 10 account for about 90% of thecross-sectional area of the support element 9 and there is therefore anairflow path through the support element 9, and through the region inwhich the brake calliper 6 is situated. Consequently transfer of heatfrom the brake ring 3 and the brake calliper 6 by convection isfacilitated. If desired, the convection can be further enhanced bymaking it forced convection, for example by providing vanes on thesupport element to drive airflow through the openings 10. This is thecase in the embodiment of FIG. 1 where the support element 9 includesvanes 11.

Removal and replacement of the wheel from the vehicle can be effected insubstantially conventional manner by first releasing and then rotating aportion of the calliper 6 about the line A-A so that it can be moved tothe position indicated by broken lines in the drawing, and then removingand subsequently replacing the fixing nuts or bolts which hold the wheelon the vehicle axle.

Vehicle braking systems in accordance with the present invention can beused on a variety of vehicles. They can be used on road vehicles, forexample cars, buses, lorries and road vehicle trailers, and they can beused on vehicles which run on rails or tracks, for example railwaycarriages, railway wagons and trams, and they can be used on aircraft.

FIG. 2 shows a modified form of wheel generally similar to that of FIG.1 with the same reference numerals designating corresponding parts. InFIG. 2 the brake ring 3 and the brake calliper 6 are not shown. Thoseparts are shown in FIG. 3. Also in FIGS. 2 and 3 the support element 9is shown having vanes 11 generating a flow of air through the wheel (asindicated by the arrows in FIG. 1).

In the embodiment shown in FIGS. 2 and 3, both the support element 9 andthe brake ring 3 are made of aluminium, a thermally conductive material.

An advantage of providing the brake ring 3 is that it adds strength tothe inner rim of the wheel allowing the thickness of parts of the wheelto be reduced.

Especially in high performance cars, it may be desirable to monitor thetemperature of the brake ring and/or the brake pads, for example with alaser thermometer (not shown) and use that temperature signal as aninput to a controller controlling the braking.

FIG. 4 shows a modified arrangement of a car in which the braking systemis mounted on rear axles 23 of a vehicle away from the wheels. In theexample shown the systems are mounted on either side of a differentialor gearbox unit 20 on which the brake callipers 21 for each of thesystems are mounted. Each braking system comprises a support element 22which is an open vaned element, which is mounted on a respective axle 23and which extends outwardly and is connected at its periphery to a brakering 3 on which the callipers 21 act. The vaned support element 22serves both to generate an airflow in the region of the brake ring 3 andthe callipers 21 and also, as a result of its fin-like structure, coolsthe support element. Arrows show the direction of airflow.

FIG. 5 shows an arrangement similar to that of FIG. 4 but applied to anaxle of a railway vehicle having wheels 25 on rails 26. The samereference numerals are used in FIG. 5 as in FIG. 4 to designatecorresponding parts.

FIG. 6 shows schematically a braking system of the kind shown in FIGS. 4and 5 with a fluid cooling system. A sealed chamber 30 is provided inthe region of the braking system and refrigerant circulated along tubes31 between the chamber 30 and another heat exchanging radiator 32 wherethe refrigerant condenses and cools. It should be understood that FIG. 6is schematic and the chamber 30 may for example only surround thecalliper and be in sealing contact with the brake ring 3.

1. A braking system comprising an axle, a support element mounted on theaxle, a brake ring connected to the periphery of the support element anda brake calliper for applying a braking force to the brake ring, thebrake ring being connected to the support element in such a manner thata conductive heat flow path is provided for conducting heat from thebrake ring into the support element and there being an airflow pathpassing through the support element and through the region in which thebrake calliper is situated for transferring heat by convection from thebrake ring and the brake calliper.
 2. A braking system according toclaim 1, wherein the support element is part of a wheel.
 3. A brakingsystem according to claim 1, further including air current generatingmeans for creating a flow of air along the airflow path.
 4. A brakingsystem according to claim 3, wherein the support element includes vanesfor creating the flow of air along the airflow path.
 5. A braking systemaccording to claim 1 wherein the brake ring is detachably connected tothe support element.
 6. A braking system according to claim 1, whereinthe brake ring is integral with the support element.
 7. A braking systemaccording to claim 1, wherein the brake ring projects radially inwardlyfrom the periphery of the support element.
 8. A braking system accordingto claim 7, wherein the brake ring is planar and is in a planeperpendicular to the axis of rotation of the axle.
 9. A braking systemcomprising an axle, a support element mounted on the axle, a brake ringconnected to the periphery of the support element and a brake calliperfor applying a braking force to the brake ring, the system furtherincluding one or more of the following features: (i) the brake ring isconnected to the support element in such a manner that a conductive heatflow path is provided for conducting heat from the brake ring into thesupport element; (ii) there is an airflow path passing through thesupport element and through the region in which the brake calliper issituated for transferring heat by convection from the brake ring and thebrake calliper; iii) the support element is part of a wheel; (iv) thebraking system includes air current generating means for creating a flowof air along the airflow path; (v) the brake ring is integral with thesupport element; (vi) the brake ring is planar and is in a planeperpendicular to the axis of rotation of the axle; (vii) the brakingsystem circulates a refrigerant system for cooling the braking system.10. A braking system according to claim 1, further including arefrigerant system for cooling the braking system.
 11. A vehicleincluding a braking system according to claim
 1. 12. A vehicle accordingto claim 11, wherein the vehicle is a car.
 13. A vehicle according toclaim 11, wherein the vehicle is a train.
 14. A vehicle according toclaim 11, wherein the vehicle is an aircraft.
 15. (canceled)